discovery.zen.minimum_master_nodes is the single most important setting to set on a production cluster. We have no way of supplying a good default so it must be set by the user. Binding a node to a public IP (as opposed to the default local host) is a good enough indication that a node will be part of a production cluster cluster and thus it's a good tradeoff to enforce the settings. Note that nothing prevent users from setting it to 1 in a single node cluster.
Closes#17288
b8227a7222